How to Build an AR-15: A Beginner’s Guide

You do not always have to go to a gun store to purchase an AR-15. Surprised? I know I was when I first ventured into the hobby of building custom AR-15s. Some of you may not know, but building your own AR-15 is actually quite simple. However, if you do not know anything about the process, or where to start, you have come to the right place. I am going to start this “How to Build an AR-15” series off with a list of frequently asked questions that I receive from individuals starting out with the hobby and possibly wanting to build their first AR-15.

WARNING! Building AR rifles is highly addictive. Once you start this process, you will find excuses to build .308 ARs, AR pistols and long range precision rifles. You have been warned.

Building an AR-15 FAQ

Q: Are there any rules or laws for building my own AR-15?A: Only the same ones that apply to purchasing a factory assembled AR-15 in your state.

Q: Do I need to register my AR-15?A: There is currently no Federal firearms registry, but you’ll need to verify the registry laws by state (e.g., New York does require registry of “assault rifles,” including standard AR-15 rifles).

Me smiling after taking some of the first shots with the first AR-15 that I built for myself. Photo of me courtesy of paul-vincent.com

Q: Do I need to be licensed or be a gunsmith to build my own AR-15?A: Not unless you’re milling the lower receiver yourself.

Q: How many AR-15s can I build?A: As many as you would like to—whichever comes first.

Q: If I build an AR-15 for myself, can I then sell it?A: The same laws for private sales of firearms apply to selling AR-15 rifles. Check your state laws.

Q: How do I buy a “stripped” or “blank” AR-15 lower receiver?A: You will need to find a dealer that sells AR-15 lower receivers. Said dealer can be local to you, or online.

Q: Can I buy all the parts online and have them shipped to my home?A: This is a long one, so get comfortable. Yes and no. All of the components for your AR-15 build can be shipped directly to you at your home except the lower receiver.

The AR-15 lower receiver is the only component that is considered the “gun”. Therefore, when purchasing a lower receiver for your AR-15 build, you will have to go through the same channels as when purchasing a firearm in your state.

For example, in my state of Minnesota, if I order a stripped AR-15 lower receiver online, I will have to provide the seller with a copy of an FFL (Federal Firearms License) and the address to aforementioned FFL. In other words, I just have to call my local gun shop and ask them to fax a copy of their FFL to the seller. The seller will then collect money from me for the receiver, and then ship it to my local gun shop. When the gun shop calls me to tell me that my lower receiver has arrived, I will go there and fill out the ATF form to make sure I can legally own a firearm, pay a transfer fee (this fee is usually less than $30), and take my new AR-15 lower receiver home (thankfully, Minnesota has no waiting period for long gun purchases).

If I decide not to order online, and I know of a gun shop that stocks lower receivers nearby, I can just go purchase it directly from that store, and then fill out the necessary ATF form, just as I would for purchasing any other kind of firearm.

Q: What parts make up an AR-15 that I would have to purchase to build one?A: There are a variety of different types of AR-15 builds, so this list will not work for all builds. However, I put together a list of components for building a typical M-4 style AR-15 with a stripped lower receiver, and stripped upper receiver:

AR-15 lower receiver.

AR-15 upper receiver.

Lower receiver parts kit.

Upper receiver parts kit.

Lower receiver extension (aka: the buffer tube).

Buffer.

Buffer spring.

Barrel & gas block/gas system (a carbine length gas system would be typical for this build).

Handguards (length will depend on what length gas system you chose on your barrel: carbine, mid-length, or rifle).

At least one magazine (be sure to check your state laws for magazine capacity limits).

Q: What is the difference between a forged lower receiver and a billet lower receiver?A: With a forged lower receiver, the metal is “smashed” into the desired form while it is red hot. This compresses the metal and makes it very strong.

Billet lower receivers are machined from a single block of metal and tend to have a more custom, aesthetically pleasing appearance to some. It also tends to have the trigger guard built in, meaning it is not removable. They also tend to cost considerably more than a forged lower. Billet lowers may not have quite the tolerance that forged lowers, but by no means are they to be considered “weak.”

This is an example of a billet AR-15 lower receiver. Image courtesy of megaarms.comThis is an example of a forged AR-15 lower receiver. Image courtesy of megaarms.com

Q: How do I know which lower receiver to purchase? What “brands” are good?A: There are a tremendous amount of different lowers out on the market, but not every lower is made by the company that has its name on the side. You would be surprised at how many lowers from different companies actually come from probably less than a dozen machine shops.

At present, this is the list of which manufacturers produce lowers for which companies:

Lewis Machine & Tool

LMT

Lauer

DS Arms

PWA

Eagle

Armalite

Knights Armament

Barrett

Continental Machine Tool

Stag

Rock River Arms

High Standard

Noveske

Century (New)

Global Tactical

CLE

S&W

MGI

Wilson Tactical

Grenadier Precision

Colt

LAR Manufacturing

LAR

Bushmaster

Ameetec

DPMS

CMMG

Double Star

Fulton Armory

Spike’s Tactical

JVP

Double Star

LRB

Charles Daly

Mega Machine Shop

Mega

GSE

Dalphon

POF

Alexander Arms

Olympic

Olympic

SGW

Tromix

Palmetto

Dalphon

Frankford

Century (Old)

Sun Devil

Sun Devil forged billet receivers

Superior

Superior Arms

Lauer (New)

Aero Precision

Aero Precision

Considering that almost all AR-15 lower receivers are made to a very specific tolerance, based on military specifications (mil-spec), my advice is to choose whichever AR-15 lower receiver that has a roll-mark (or logo) that you think is “coolest” or is most appealing to you personally.

Q: Some barrels say they are chambered in 5.56 and some say they are chambered in .223. What is the difference?A: Basically, the rule of thumb is this: a rifle chambered for 5.56 can shoot both 5.56 and .223 ammunition. A rifle chambered for .223 can only shoot .223 and not 5.56. For the full story on 5.56 vs. .223, check out this article by Destinee.

Q: What does barrel twist mean? 1:7 and 1:9? Ratio? What?A: Confused? Yeah, this one is kind of technical but I will keep it simple. When choosing a barrel twist ratio, you will want to choose one that best matches the type of ammo you would normally be shooting. What the ratio means, such as 1:7 for example, is that when the bullet travels down the barrel, it will make one complete spin (via the rifling) every seven inches.

(Fig. 1a)This is great information about shooting 1:7 vs. 1:9 twist ratios at long distances through your AR-15.

This is one of the most hotly debated topics about AR-15 rifles. Personally, I chose to go with 1:7 because it gives me the option of shooting the heavier rounds. Because 55gr .223/5.56 is the most common bullet weight available (that’s the weight used in XM193 military ball 5.56×45 ammo), and the most frequently fired, you would be fine with either 1:7 or 1:9. I have also been told by reputable sources in law enforcement that 1:9 is recommended for plinking, and 1:7 for hunting and home defense.

To break it down, 1:7 will do just fine with shooting lighter and heavier rounds. 1:9, on the other hand, will handle lighter rounds better, and will not do so well with anything heavy at long distances. (Fig. 1a)

A comparison photo of different length gas systems, barrels and rail systems for an AR-15. Image courtesy of laruetactical.com

Q: What does carbine, mid-length and rifle length mean when choosing a barrel?A: It simply means where the gas port in the barrel is placed. It is also sometimes referred to as the “gas-system”. Carbine and mid-length gas systems tend to be on barrels of 16-18 inches and shorter, while barrels with a length of 20 inches and longer will have a rifle length gas system.

It is important to know what length gas system your barrel has because the gas tube you purchase will need to be the right length in order to fit properly. For example, you cannot fit a carbine length gas tube onto a barrel with a rifle length gas system. The gas tube will be too short.

Q: I am ready to build my AR-15 lower receiver but I do not know the steps. How do I do it?A: Great question. In the following posts in this “How to Build an AR-15” series, I will go over how to build your AR-15 (starting with building your lower receiver, and moving from there to the AR-15 upper), what tools you will need, and I’ll offer some helpful tips along the way. Stay tuned.

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About the Author

Nate Schultz
Nate Schultz is employed within the field of Law Enforcement, is an avid shooter, firearms enthusiast and hobbiest gunsmith. When he is not writing for The Arms Guide, he is producing content for his YouTube channel: www.youtube.com/nsz85